Key comparison CCAUV.W-K2: features of hydrophone calibration

The results of a key comparison are considered, which are the most convincing and objective indicators confirming the correctness and accuracy of the measurement method developed and applied in comparisons. The article describes comparison results and measurement methods applied in the second key comparison of national standards for sound in water CCAUV.W-K2, which was organized by the Consultative Committee for Acoustics, Ultrasound, and Vibration of the International Bureau of Weights and Measures. A special feature of these comparisons is that the calibration range is extended down by two octaves to the low-frequency region as compared to the first key comparisons CCAUV.W-K1. The results of CCAUV.W-K2 were found to be successful. Important scientific results of participating in these comparisons included the confirmed correctness of free-field hydrophone calibration methods (at super low frequencies for a sound-reflecting water tank and in the reverberant noise sound field of the water tank) developed at the Russian Metrological Institute of Technical Physics and Radio Engineering, as well as the equivalence of calibration results with radiation of different kinds of signals—chirp, noise, and tone-burst. In the process of performing check calibrations, the pilot laboratory discovered the destabilization of the reference hydrophone used in the comparison. A comparison of the results obtained by the participants revealed an increase in the discrepancy between results within the 60–100 kHz frequency region, which is considered to be the least problematic.